# What is meant by “the current-voltage characteristic was asymmetric and non-ohmic”?

I am currently studying the textbook Light-Emitting Diodes (3rd Edition) by E. Fred Schubert. Chapter 2.1 Compound semiconductors says the following:

In 1874, Karl Ferdinand Braun (1874), a German scientist, reported on the electrical conduction in metal-semiconductor structures where the semiconductor was a metal sulfide such as ZnS, PbS, FeS$$_2$$, and CuFeS$$_2$$. He found that the current-voltage characteristic was asymmetric and non-ohmic and thus exhibited some degree of rectification. His work is the first demonstration of the rectifying properties of metal-semiconductor contacts and the first scientific research in compound semiconductors.

What is meant by "the current-voltage characteristic was asymmetric and non-ohmic", and why does this mean that the semiconductor exhibits some degree of rectification?

Ohmic would mean means it follows Ohm's law $$\ I= {\mathcal{E} \over R}$$